Surreal vineyard with glowing beakers representing the chemical balance in winemaking.

Sherry Winemaking: Unlocking the Secrets of Acidification for the Perfect Taste

Reese Marlowe in Science & Nature August 2025 • 4 min read.

"Mastering Acidity in Sherry: A Comprehensive Guide to Calcium Sulphate and Tartaric Acid"

In the world of winemaking, achieving the perfect balance is an art and a science. One crucial aspect of this balance is acidity, which significantly impacts the taste, stability, and color of the final product. Acidification, the process of reducing pH levels in musts (unfermented grape juice), is particularly vital in warmer regions where grapes tend to lose acidity during ripening.

Traditionally, winemakers have relied on L(+)-tartaric acid to adjust acidity. However, modern regulations also permit the use of L-malic acid, D,L-malic acid, and lactic acid. In Sherry production, calcium sulphate (CaSO4.2H2O) plays a unique role, often used in conjunction with tartaric acid to fine-tune the must's chemical composition. This practice reduces the amount of tartaric acid needed, contributing to a distinct flavor profile.

This article explores the comprehensive chemical study of must acidification in the Sherry region, focusing on the use of calcium sulphate and tartaric acid. We'll delve into the methods, results, and sensory impacts of this delicate balancing act, providing insights for both seasoned winemakers and enthusiasts alike. Understanding these processes is key to producing high-quality Sherry with the desired characteristics.

The Chemistry Behind Acidification: How Calcium Sulphate and Tartaric Acid Work Together

Surreal vineyard with glowing beakers representing the chemical balance in winemaking.

The precise control of pH is essential in winemaking. A lower pH inhibits bacterial activity, stabilizes color, and enhances the wine's sensory characteristics. In warmer climates, high temperatures during grape ripening accelerate the combustion of tartaric and malic acids, necessitating careful acidification.

Calcium sulphate's role in must acidification is based on its interaction with tartrate ions. The addition of calcium ions (Ca2+) leads to the precipitation of calcium tartrate, releasing hydrogen ions (H+) and lowering the pH:

Ca2+ + H2T → CaT ↓+ 2H+

This reaction reduces both tartrate and ash alkalinity (AA), which are crucial components in maintaining the balance. The amount of calcium sulphate added directly influences the final pH, necessitating careful calculations to achieve the desired acidity without exceeding regulatory limits.

Achieving the Perfect Sherry: Sensory Analysis and the Future of Acidification

Ultimately, the goal of must acidification is to create a Sherry that not only meets chemical standards but also delights the senses. Sensory analysis reveals that the combination of calcium sulphate and tartaric acid often leads to a more balanced and preferred taste profile compared to using tartaric acid alone. This highlights the importance of understanding the complex chemical equilibria involved in this practice, ensuring that the final product is both stable and enjoyable.

About this Article -

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This article is based on research published under:

DOI-LINK: 10.1051/bioconf/20160702023, Alternate LINK

Title: Comprehensive Chemical Study Of The Acidification Of Musts In Sherry Area With Calcium Sulphate And Tartaric Acid

Journal: BIO Web of Conferences

Publisher: EDP Sciences

Authors: J. Gómez, C. Lasanta, L. M. Cubillana-Aguilera, J. M. Palacios-Santander, R. Arnedo, J.A. Casas, B. Amilibia, I. Lloret

Published: 2016-01-01

Everything You Need To Know

What is acidification in the context of Sherry winemaking, and why is it necessary?

Acidification in Sherry winemaking is the process of lowering the pH levels in musts (unfermented grape juice). This is particularly important in warmer regions where grapes tend to lose acidity as they ripen. This process involves carefully balancing the use of calcium sulphate and tartaric acid to achieve the desired flavor profile and stability in the final Sherry product.

How does calcium sulphate contribute to the acidification process in Sherry production?

Calcium sulphate (CaSO4.2H2O) works by interacting with tartrate ions in the must. When added, the calcium ions (Ca2+) cause the precipitation of calcium tartrate, which releases hydrogen ions (H+), thus lowering the pH. This process reduces both tartrate and ash alkalinity (AA), which are essential components in maintaining the chemical balance of the must. Careful calculation is needed to ensure the right amount of calcium sulphate is added without exceeding regulatory limits.

Why do Sherry winemakers use calcium sulphate in combination with tartaric acid?

Winemakers use calcium sulphate in conjunction with tartaric acid to fine-tune the chemical composition of the must. By adding calcium sulphate, they can reduce the amount of tartaric acid needed to achieve the desired acidity level. Sensory analysis has shown that this combination often leads to a more balanced and preferred taste profile in the final Sherry compared to using tartaric acid alone.

Why is precise control of pH so important in Sherry winemaking, and what can happen if acidification is not properly managed?

The precise control of pH is crucial because a lower pH inhibits bacterial activity, stabilizes the color of the wine, and enhances its sensory characteristics. In warmer climates, high temperatures during grape ripening accelerate the combustion of tartaric and malic acids, necessitating careful acidification to maintain the wine's quality and desired profile. Failing to acidify properly can lead to instability, off-flavors, and undesirable color changes.

Besides tartaric acid and calcium sulphate, what other acids are permitted for acidification, and what are their specific roles in Sherry production that are not discussed here?

Modern regulations permit the use of L-malic acid, D,L-malic acid, and lactic acid for acidification, in addition to the traditionally used L(+)-tartaric acid. While not directly discussed, the specific applications and benefits of each acid in the context of Sherry production can be explored further. Understanding the nuances of each acid's impact on flavor, stability, and regulatory compliance is essential for winemakers aiming to produce exceptional Sherry.